The present invention is generally related to vehicle speed sensors. The present invention is also related to automotive applications that utilize vehicle speed sensors to sense gears or other rotating members. The present invention is also related to vehicle speed sensor conditioning circuits. The present invention is additionally related to methods and systems for improving the duty cycle output of vehicle speed sensors utilized in automotive applications.
Many modern automotive, marine and other vehicles are equipped with electronic control systems that regulate various components of the vehicle. These electronic control systems are utilized to control the components based on information represented by output signals from various sensors for detecting operating conditions. A vehicle speed sensor is a device, which is generally utilized in an automobile to sense vehicle speed and send this information to the vehicle""s onboard computer. In order to control engine performance electronically, it is often necessary to provide a variety of signals to the engine control module. These signals indicate the status of the parameter being detected and to which the control must respond. Among status signals necessary is a signal that is indicative of the vehicle speed.
Transmission-mounted vehicle speed sensors, for example, can be utilized to sense the speed of a vehicle. Transmission manufacturers provide a means of generating a signal, which is proportional to the rate of rotation of the drive shaft. This is accomplished by placing a tone wheel (i.e., a wheel), which has about its circumference lands and valleys that may be of equal width and are generally in line with the power take-off shaft. The signal which is indicative of the vehicle shaft rotation is generated by inserting a vehicle speed sensor into a port opposite the face of the tone wheel until the sensor comes in contact with the face of the tone wheel, then backed off a half turn or to an orientation mark. The gap between the land of the tone wheel and the sensor tip is usually approximately 0.050 (fifty thousandths) of an inch. As the tone wheel rotates, the lands and valleys alternately pass over the sensor head. Each time a land passes, the gap is approximately fifty thousandths of an inch. Each time a valley passes, the gap increases to as much as a quarter of an inch. Those skilled in the art can appreciate that these values are approximations and can vary from application to application. The changes in gap size change the magnetic field concentration between the sensor head and the tone wheel. This change in magnetic field concentration causes a self-induction process to take place within the sensor winding, which in turn causes a voltage to appear at the coil""s output leads. This voltage is semi-sinusoidal and the frequency and voltage amplitude is proportional to the rotational speed of the tone wheel.
Also, vehicle speed sensors that use a Hall-effect device as the signal-generating element have been utilized. These have the advantage of generating a signal of uniform amplitude over the entire vehicle speed range. Such a signal may also be configured as a digital output as opposed to a sine type wave, which may be obtained from a VRS (i.e., electromagnetic) sensor. Additional circuitry may be implemented to include an analog or sinusoidal-type input signal that can vary in amplitude. These too were applied as described above. The transducer body contains a Hall-effect sensing element, which is magnetically biased by a permanent magnet mounted in communication with and immediately behind the sensor. The face of the sensing element is approximately 0.015 inches from the end of the sensor body face. As the transducer is screwed into the transducer port of the transmission, it is driven in until it bottoms out against the tone wheel and is then backed off until an orientation mark aligns in line with the tone wheel. Note that some sensors do have a fixed reach air gap designed therein; thus, the aforementioned xe2x80x9cbump and back upxe2x80x9d process is unnecessary. Note, too, that the sensor may be mounted by means other than forming a hole through which the transducer is screwed. The orientation is important because the Hall-effect sensing element is position sensitive; the orientation is only critical, however, on differential Hall sensors. Some single element Hall sensors are not rotationally sensitive. There are also magnetoresistive types of sensors that can sense gear teeth. For instance, certain types of RF coil proximity sensors can be utilized as gear tooth sensors as well. The resulting gap between the tone wheel and the sensing element is usually less than, for example, 0.050 inches. Other air gap distances, of course, may be achieved; the value 0.050 inches thus represents an illustrative example.
For mechanisms having one portion that rotates relative to another, it is often necessary to know the precise relative rotational position between the two portions. There are many types of sensor arrangements that can accomplish such a task; however, many have drawbacks in that they are too large for a particular application, too expensive to design and fabricate, or require extensive calibration once assembled in the mechanism. These types of sensors can be used, for example, as throttle position sensors, fuel accumulators, transmission position sensors, steering angle sensors, and gear tooth sensors. Many other types of applications of course can also benefit from having rotational position sensing.
Wheel speed detecting components can be based on electromagnetic configurations having excellent environmental resistance. A sensor ring, for example, of a magnetic material having a gear shaped surface of high gear tooth pitch accuracy can be employed for implementation in a speed detecting system. FIG. 1 illustrates a prior art front elevational view of a sensor ring. FIG. 2 depicts a prior art sectional view taken along the line Bxe2x80x94B depicted in FIG. 1. Finally, FIG. 3 illustrates an enlarged prior art view illustrating a portion C in FIG. 1. FIG. 4 depicts a diagram generally illustrating a prior art operational principle of electromagnetic wheel speed detection utilizing the sensor ring shown in FIG. 1.
As depicted in FIG. 4, the sensor ring 21 is mounted on a wheel to have a constant clearance between a pole piece 23 of a sensor coil 22 and each tip of the sensor ring 21. The electromagnetic coil 22 receives the magnetic flux change, which is caused in the changing clearance between the coil 22, and the successive tips and grooves of the gear teeth during rotation of the wheel. The coil 22 correspondingly generates an excited output voltage 25 which can be detected to correctly read the speed of each wheel.
Vehicle speed sensors, such as the wheel speed sensor configuration illustrated in FIGS. 1 to 4, are thus utilized in automotive applications to sense gears or other rotating members, such as ring magnets. Such gears are usually located in the vehicle transmission. A vehicle speed sensor thus can provide a digital pulse type output for every gear tooth that passes in front of the sensor.
It is desirable to configure a vehicle speed sensor circuit to provide a certain exact number of pulses per miles of vehicle travel. Because of different transmission gear ratios, wheel sizes, and so forth, it is often necessary to utilize different sensor actuation gears to achieve a correct number of pulses per mile from the vehicle speed sensor. Utilizing different gears in different vehicles increases complexity and cost.
It is also often a requirement of vehicle speed sensor users to obtain an output duty cycle at or very near a fifty-percent (50%) duty cycle. This is difficult to achieve because the sensor output duty cycle is dependent on many variables, the largest of which is the sensor-to-target air gap. The sensor-to-target air gap is difficult to control in the vehicle.
The present inventor has thus concluded, based on the foregoing, that a need exists for an improved vehicle speed sensor circuit, which would improve the output duty cycle at or very near a 50% duty cycle. The invention disclosed herein addresses this need by providing an improved vehicle speed sensor conditioning circuit, including methods and systems thereof.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is, therefore, one aspect of the present invention to provide an improved vehicle speed sensor.
It is another aspect of the present invention to provide improved methods and systems for implementing vehicle speed sensors in automotive applications in order to sense gears or other rotating members.
It is also an aspect of the present invention to provide a vehicle speed sensor conditioning circuit.
It is yet another aspect of the present invention to provide methods and systems for improving the duty cycle output of vehicle speed sensors utilized in automotive applications.
The above and other aspects are achieved as is now described. Methods and systems for improving the duty cycle output of a vehicle speed sensor circuit are disclosed. The vehicle speed sensor circuit can be configured to provide a particular number of pulses per distance of vehicle travel. An output of the vehicle speed sensor circuit is generally divided by placing varying values on particular load pins of an associated counter circuit, thereby providing a substantially improved duty cycle output from the vehicle speed sensor circuit, which is independent of an associated sensor duty cycle. The particular load pins can be parallel load pins. The associated counter circuit can be configured as a binary counter. The output of the vehicle speed sensor circuit can be divided utilizing a toggle flip-flop circuit integrated with the vehicle speed sensor circuit. The toggle flip-flop can be configured as an edge-triggered toggle flip-flop, which can trigger on negative edges, such that negative edge spacing is independent of a sensor air gap associated with the vehicle speed sensor circuit, thereby achieving a duty cycle output from the vehicle speed sensor circuit that functions constantly at an approximately fifty-percent duty cycle. The vehicle speed sensor can be utilized to sense rotating members present in a vehicle. The rotating members may form gears, such that the gears are configured to include gear teeth. The vehicle speed sensor thus provides a digital pulse output for every tooth that passes in front of the vehicle speed sensor. The vehicle itself may be, for example, an automobile.